Re: Top 5 Gaming series
Gran Turismo (no other driving sim/racing game even comes close...)
Elite (good call, Urlik! I spent hundreds of hours playing those games!)
Doom (genre-defining, yada yada...)
Championship/Football Manager (thousands of hours, srsly...)
Sonic (representing my youth... ;p)
Obviously if I had been allowed to say Final Fantasy, it would have topped everything. Others, such as GTA, Guitar Hero, Civ, Age of Empires, SimCity, etc, deserve a mention.
Others still, like MGS, I have only played one of, and so can't really comment. If I had played the (proper) sequel to Strider I might have mentioned it, since I loved that game.